/**
 *create by 2014年7月9日 http://javascript.css-js.com/
 *BASE64 Encode and Decode By UTF-8 unicode
 *可以和java的BASE64编码和解码互相转化
 */
  var BASE64_MAPPING = [
    'A','B','C','D','E','F','G','H',
    'I','J','K','L','M','N','O','P',
    'Q','R','S','T','U','V','W','X',
    'Y','Z','a','b','c','d','e','f',
    'g','h','i','j','k','l','m','n',
    'o','p','q','r','s','t','u','v',
    'w','x','y','z','0','1','2','3',
    '4','5','6','7','8','9','+','/'
  ];
  /**
   *ascii convert to binary
   */
  var _toBinary = function(ascii){
    var binary = new Array();
    while(ascii > 0){
      var b = ascii%2;
      ascii = Math.floor(ascii/2);
      binary.push(b);
    }
    /*
    var len = binary.length;
    if(6-len > 0){
      for(var i = 6-len ; i > 0 ; --i){
        binary.push(0);
      }
    }*/
    binary.reverse();
    return binary;
  };
  /**
   *binary convert to decimal
   */
  var _toDecimal = function(binary){
    var dec = 0;
    var p = 0;
    for(var i = binary.length-1 ; i >= 0 ; --i){
      var b = binary[i];
      if(b == 1){
        dec += Math.pow(2 , p);
      }
      ++p;
    }
    return dec;
  };
  /**
   *unicode convert to utf-8
   */
  var _toUTF8Binary = function(c , binaryArray){
    var mustLen = (8-(c+1)) + ((c-1)*6);
    var fatLen = binaryArray.length;
    var diff = mustLen - fatLen;
    while(--diff >= 0){
      binaryArray.unshift(0);
    }
    var binary = [];
    var _c = c;
    while(--_c >= 0){
      binary.push(1);
    }
    binary.push(0);
    var i = 0 , len = 8 - (c+1);
    for(; i < len ; ++i){
      binary.push(binaryArray[i]);
    }
    for(var j = 0 ; j < c-1 ; ++j){
      binary.push(1);
      binary.push(0);
      var sum = 6;
      while(--sum >= 0){
        binary.push(binaryArray[i++]);
      }
    }
    return binary;
  };
  var BASE64 = {
      /**
       *BASE64 Encode
       */
      encoder:function(str){
        var base64_Index = [];
        var binaryArray = [];
        for(var i = 0 , len = str.length ; i < len ; ++i){
          var unicode = str.charCodeAt(i);
          var _tmpBinary = _toBinary(unicode);
          if(unicode < 0x80){
            var _tmpdiff = 8 - _tmpBinary.length;
            while(--_tmpdiff >= 0){
              _tmpBinary.unshift(0);
            }
            binaryArray = binaryArray.concat(_tmpBinary);
          }else if(unicode >= 0x80 && unicode <= 0x7FF){
            binaryArray = binaryArray.concat(_toUTF8Binary(2 , _tmpBinary));
          }else if(unicode >= 0x800 && unicode <= 0xFFFF){//UTF-8 3byte
            binaryArray = binaryArray.concat(_toUTF8Binary(3 , _tmpBinary));
          }else if(unicode >= 0x10000 && unicode <= 0x1FFFFF){//UTF-8 4byte
            binaryArray = binaryArray.concat(_toUTF8Binary(4 , _tmpBinary));  
          }else if(unicode >= 0x200000 && unicode <= 0x3FFFFFF){//UTF-8 5byte
            binaryArray = binaryArray.concat(_toUTF8Binary(5 , _tmpBinary));
          }else if(unicode >= 4000000 && unicode <= 0x7FFFFFFF){//UTF-8 6byte
            binaryArray = binaryArray.concat(_toUTF8Binary(6 , _tmpBinary));
          }
        }
        var extra_Zero_Count = 0;
        for(var i = 0 , len = binaryArray.length ; i < len ; i+=6){
          var diff = (i+6)-len;
          if(diff == 2){
            extra_Zero_Count = 2;
          }else if(diff == 4){
            extra_Zero_Count = 4;
          }
          //if(extra_Zero_Count > 0){
          // len += extra_Zero_Count+1;
          //}
          var _tmpExtra_Zero_Count = extra_Zero_Count;
          while(--_tmpExtra_Zero_Count >= 0){
            binaryArray.push(0);
          }
          base64_Index.push(_toDecimal(binaryArray.slice(i , i+6)));
        }
        var base64 = '';
        for(var i = 0 , len = base64_Index.length ; i < len ; ++i){
          base64 += BASE64_MAPPING[base64_Index[i]];
        }
        for(var i = 0 , len = extra_Zero_Count/2 ; i < len ; ++i){
          base64 += '=';
        }
        return base64;
      },
      /**
       *BASE64 Decode for UTF-8 
       */
      decoder : function(_base64Str){
        var _len = _base64Str.length;
        var extra_Zero_Count = 0;
        /**
         *计算在进行BASE64编码的时候，补了几个0
         */
        if(_base64Str.charAt(_len-1) == '='){
          //alert(_base64Str.charAt(_len-1));
          //alert(_base64Str.charAt(_len-2));
          if(_base64Str.charAt(_len-2) == '='){//两个等号说明补了4个0
            extra_Zero_Count = 4;
            _base64Str = _base64Str.substring(0 , _len-2);
          }else{//一个等号说明补了2个0
            extra_Zero_Count = 2;
            _base64Str = _base64Str.substring(0 , _len - 1);
          }
        }
        var binaryArray = [];
        for(var i = 0 , len = _base64Str.length; i < len ; ++i){
          var c = _base64Str.charAt(i);
          for(var j = 0 , size = BASE64_MAPPING.length ; j < size ; ++j){
            if(c == BASE64_MAPPING[j]){
              var _tmp = _toBinary(j);
              /*不足6位的补0*/
              var _tmpLen = _tmp.length;
              if(6-_tmpLen > 0){
                for(var k = 6-_tmpLen ; k > 0 ; --k){
                  _tmp.unshift(0);
                }
              }
              binaryArray = binaryArray.concat(_tmp);
              break;
            }
          }
        }
        if(extra_Zero_Count > 0){
          binaryArray = binaryArray.slice(0 , binaryArray.length - extra_Zero_Count);
        }
        var unicode = [];
        var unicodeBinary = [];
        for(var i = 0 , len = binaryArray.length ; i < len ; ){
          if(binaryArray[i] == 0){
            unicode=unicode.concat(_toDecimal(binaryArray.slice(i,i+8)));
            i += 8;
          }else{
            var sum = 0;
            while(i < len){
              if(binaryArray[i] == 1){
                ++sum;
              }else{
                break;
              }
              ++i;
            }
            unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+1 , i+8-sum));
            i += 8 - sum;
            while(sum > 1){
              unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+2 , i+8));
              i += 8;
              --sum;
            }
            unicode = unicode.concat(_toDecimal(unicodeBinary));
            unicodeBinary = [];
          }
        }
        //---------直接转换为结果
        var strResult = ''; 
        for(var i = 0 , len = unicode.length ; i < len ;++i){ 
           strResult += String.fromCharCode(unicode[i]); 
        }
        return strResult;
      }
  };
  
  module.exports = BASE64